Spiral sheath retainer for autoperfusion dilatation catheter balloon

ABSTRACT

A spiral balloon perfusion catheter assembly having a retaining wire and method of making the balloon. Also, a retaining wire for such a catheter and method of forming the retaining wire. A typical spiral catheter balloon has a spiral configuration of lobes and channels mounted on a catheter extending beyond the balloon ends. A retaining wire formed from a shape memory alloy is configured to have a central region having a spaced spiral configuration conforming to the spiral balloon channel and end regions configured to have a contiguous spiral configuration conforming to the catheter diameter. When placed over a spiral balloon, the central spiral region prevents expansion of the channel when the balloon is inflated, while the end regions secure the retaining wire to the catheter. Preferred shape memory alloys comprise nickel and titanium. The retaining wire is made by heating the wire above the crystal phase change temperature of the alloy, shaping the spirals then cooling the product below the crystal phase change temperature. The spiral end regions may be unwound and placed over the catheter adjacent to the balloon with the wire in the central spiral region conforming to the balloon channel.

This application is a Divisional of application Ser. No. 08/685,302filed Jul. 23, 1996, now U.S. Pat. No. 5,735,816.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for improving theperformance of autoperfusion dilatation catheters as used in angioplastyand the like, and more specifically to an arrangement for maintaining aspiral sheath configuration during those procedures.

Dilatation balloon catheters are well known and used regularly forcoronary angioplasty procedures and other similar procedures.Atheromatous plaque adhering to a blood vessel wall and restrictingblood flow therethrough is compressed against the vessel wall by aballoon that is positioned in the vessel at the plaque location. Thisdilates the vessel lumen to permit increased blood flow.

A typical balloon catheter includes two lengthwise lumens or channels,one for inflation of an inflatable balloon sealed to the distal catheterend and the other for insertion of a guidewire extending though thecatheter to aid in positioning the catheter during use.

Many catheters have been designed for particular uses, having a varietyof configurations, methods of construction and methods of use. Most havea generally tubular balloon that, when inflated, temporarily cuts offblood flow through the vessel. Serious consequences can occur when bloodflow is stopped for an extended period. Therefore, inflation duration isgenerally relatively short, typically no more than 150-180 seconds.Longer inflation periods would be very desirable, since better plaquecompression could be accomplished. Also, some patients cannot tolerateeven short time blood occlusion in some vessels.

Attempts have been made to develop balloon configurations that willpermit at least some continued blood flow during plaque compression. Forexample, catheters having an additional lumen have been used, withopenings between the catheter exterior and the added lumen at both endsof the balloon, so that limited blood flow can bypass the balloonocclusion. However, this arrangement has had limited success, since onlya very limited amount of blood can flow though the lumen and adding thelumen increases the diameter of the catheter, which itself will tend toretard blood flow. Thus, at most this arrangement will allow a veryslightly longer balloon inflation period.

Fogarty et al. in U.S. Pat. No. 4,762,130, Blackshear et al. in U.S.Pat. No. 5,308,356 and others have disclosed catheter balloons with aspiral or corkscrew-like configuration when expanded. Such perfusionballoon catheters are intended to allow blood to flow in a spiralchannel path past the balloon during balloon inflation. However, inpractice, little if any blood flow is found to occur with these spiralballoons, apparently due to blockage of the balloon channels by thearterial intima or lining and/or expansion of the balloon in the channelregion decreasing channel cross sectional area.

Attempts have been made to reinforce the channel of a spiral catheterballoon with a spiral metal or plastic wire engaging the balloon spiralchannel, as described by Gurbel et al. in U.S. Pat. No. 5,295,959 andInderbitzen et al. in U.S. Pat. No. 5,484,411.

These reinforcing wires have been less than fully successful, primarilybecause expansion of the balloon tends to stress the wire to the pointwhere the channel shape is not retained and the wire is stretched beyondits elastic limits. Further, the wire may be excessively bent whilenegotiating tortuous paths while the balloon catheter is being emplaced.Where the wire has been stressed to the point where the modulus ofelasticity is exceeded the balloon cannot be returned to its originaldiameter during rewrapping, making the balloon difficult and dangerousto withdraw. In addition, where the wire is simply bonded to the balloonor wrapped around the catheter adjacent to the balloon ends, the bondmay be released or the end wraps may unwrap, when the balloon isexpanded, resulting in a loose or partially loose wire, which can bevery difficult to remove from a body lumen.

Thus, there is a continuing need for improved spiral catheter balloonsincluding a spiral channel retainer that will maintain sufficientperfusion capacity while the balloon is inflated, that will maintain thechannel shape during inflation, that will not become permanentlydeformed during catheter movement through a tortuous lumen path, thatwill return fully to the uninflated diameter and shape when deflated andthat will remain securely attached to the catheter during balloonemplacement, inflation, deflation and withdrawal.

SUMMARY OF THE INVENTION

The above-noted problems, and others, are overcome in accordance withthis invention by spiral balloon perfusion catheter assembly thatbasically comprises a catheter having a balloon configured in anexterior spiral lobe and channel pattern and a wire retainer secured tothe catheter and having a spiral region lying along the balloon channelsto retain the channel shape during balloon inflation. The wire retaineris formed from a shape memory alloy, preferably a alloy having selectedproportions of nickel and titanium.

The wire retainer has a center region with a spaced spiral conforming tothe balloon channel. Preferably the spiral is cylindrical in over allconfiguration, with a straight axis. End regions are configured ascylindrical contiguous spirals, with the inside diameter of thecylindrical spiral conforming to the exterior diameter of the catheteradjacent to the balloon. Preferably, the wire is configured with abasically rectangular, flat, cross section with the wire width generallyparallel to the spiral axis. A round wire, typically having a diameterof from about 0.002 to 0.006 inch or a narrow flat wire may be used.Preferably, the wire is flat with a width of from about 0.02 to 0.03inch and a thickness of from about 0.002 to 0.005 inch. Wire edges arepreferably rounded.

The wire retainer is preferably made by heating the wire above thecrystal phase change temperature, to the Austenite state, and shapingthe wire to the desired spiral configuration in the central and endregions, typically by wrapping on a suitable cylindrical mandrel. Thesections for the different regions may have the same or differentdiameters and pitches to produce corresponding cylindrical spirals. Onceshaping is complete, the wire is cooled to a temperature below thecrystal phase change temperature, to the Martensite state. Anickel-titanium alloy having a crystal phase change temperature wellabove room temperature is preferred. The resulting product can beseverely flexed, such as by unwinding an end spiral and fitting it overa catheter, without permanent deformation. In addition the wire retaineris highly resistant to deformation, to resist expansion in the centralregion during balloon inflation, so that the channels are keptsubstantially open.

Once the wire retainer is mounted on the balloon and catheter, the endregion contiguous spirals are preferably encapsulated. Any suitableencapsulation may be used, such as impregnation with an adhesive such asa UV curing adhesive, a cyanoacrylate or an epoxy, enclosure in a heatshrink tube or covering with tape. For convenience and effectiveness,adhesives are preferred.

It is, therefore, an object of this invention to provide a spiralballoon perfusion catheter assembly which provides improved perfusionduring dilation. Another object is to provide a retaining wire forspiral balloons that when emplaced on such a balloon will maintain asubstantially constant channel configuration during balloon inflation. Afurther object is to provide a retaining wire for spiral balloons thatwill resist permanent deformation during balloon catheter insertion intoa body lumen and during balloon inflation. Yet another object is toprovide a retaining wire that is more securely attached to a catheteradjacent to a balloon. A further object is to provide a convenient andrapid method of making a spiral balloon perfusion catheter assemblyhaving improved perfusion performance. Still another object is toprovide convenient and rapid methods of making an improved spiralballoon channel retaining wire.

BRIEF DESCRIPTION OF THE DRAWING

Details of the invention, and of preferred embodiments thereof, will befurther understood upon reference to the drawing, wherein:

FIG. 1 is a side elevation view, partly cut away, of a spiral balloonperfusion catheter assembly of this invention;

FIG. 2 is a side elevation view of a wire retainer for use in a spiralballoon perfusion catheter assembly; and

FIG. 3 is a section view taken on line 3--3 in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, there is seen a spiral balloon perfusion catheterassembly 10, including a conventional catheter 12, an inflatable spiralballoon 14 and a sheath 16 over balloon 14.

Any suitable catheter 12 may be used. Typically, catheter 10 may includea polymer tube incorporating a body spring and having one or more lumensfor passage of a guidewire, a channel for a fluid to inflate theballoon, etc.

Balloon 14 is wrapped to provide a small cross section for insertion ina body lumen. When positioned at a desired location, balloon 14 isinflated to assume the configuration shown in FIG. 1. The spiralconfiguration of lobes 18 and channels 20 permits perfusion of bloodpast the balloon, permitting inflation for longer periods withoutexcessively slowing blood flow.

A sheath 16 is preferably provided over balloon 14 and bonded thereto toprevent arterial intima from entering and at least partially blockingchannels 20. Sheath 16 includes ribs 22 extending from the ends of theballoon-engaging sheath portion and collars 24 for securing the ends ofribs 22 to catheter 12.

A wire retainer 26 is provided to maintain channels 20 at the properdepth and prevent expansion of those channels during balloon inflation,with the corresponding reduction in perfusion path cross section. Wireretainer 26 has a spaced spiral center region 28 conforming in shape tochannels 20 and radially wound contiguous end regions 30 configured toprovide an interference fit over catheter 12 adjacent to the ends ofballoon 14. The inside diameters of end regions 30 may be the same ordifferent, depending upon the outside diameters of catheter 12 at theends of balloon 14.

In order to fully resist expansion forces during inflation of balloon 14while permitting easy assembly of the balloon and wire retainer 26, thewire retainer is formed from a shape memory alloy. Any suitable shapememory alloy may be used. Typically, suitable alloys primarily comprisenickel and titanium. Typical preferred proportions are about 55.7 wt %nickel and about 43.9 wt % titanium and trace amounts of other elements,e.g. chromium, carbon, oxygen, hydrogen. Such alloys are commerciallyavailable from Dynaloy, Inc., Shape Memory Applications, Inc. andothers.

In order to constrain the bottoms of channels 20 in an optimum manner,the wire retainer 26 preferably has a generally rectangular to ovalcross section, with the longer side lying generally parallel to theballoon axis. Widths of from about 0.02 to 0.03 inch and thicknesses offrom about 0.002 to 0.005 inch are generally optimum. The edges of thewire retainer are preferably rounded by any suitable method, such aschemical etching. If desired, the wire retainer may be bonded to thebottom of channel 20 such as by an adhesive, heat sealing or the like.

Along channels 20, wire retainer 26 has a central region with acylindrical spiral configuration matching that of the channels. At theends of the central region, wire retainer 26 transitions to a contiguousradially wound form corresponding to catheter diameter in end regions.For best results, the wire retainer in the end regions 30 is wrapped toform from about 1.5 to 3 coils. Optimally, about 2.5 end region turnsare provided at the proximal end of balloon 14 and about 2 turns at thedistal end with the wire dimensions described above. With relativelysmall cross section wire, the number of coils may be increased to up to6 to 10 coils.

In order to positively prevent any unraveling of the wire retainer 26end region coils 30 during full inflation of balloon 14, those coils arepreferably encapsulated. The encapsulation of end region coils 30reinforce the retention of the wire retainer on the catheter whenballoon 14 is inflated to high pressure and creates a more uniform,smooth, surface to aid insertion and removal of the catheter. Typically,an adhesive such as an epoxy or cyanoacrylate, a heat shrinkable sleeve,tape, etc., could be used. Of these, Loctite ® (manufactured by LoctiteCorp. in Hartford Conn.) #406 is preferred because of its high tensileand peel strength and rapid cure.

The wire retainer is made by wrapping the shape memory alloy wire ontoan appropriately configured mandrel while heating the wire above thetransition temperature. The mandrel has diameters over selected lengthscorresponding to the spiral central region 28 and each radial end region30. Typically, an end of the wire may be inserted into a hole in themandrel and the opposite end grasped in pliers. While heating, the wireis wrapped in the desired pattern around the mandrel, then cooled belowthe transition temperature. After the mandrel is cooled, excess wire istrimmed away and the wire retainer 26 is carefully unwound from themandrel. Wire retainer 26 is then installed on a balloon 14 by wrappingthe center region 28 and fitting it into channels 20. Each end region 30is then unrolled and rerolled over catheter 12 adjacent to balloon 14.The end region coils are then encapsulated, if desired, and sheath 16 isinstalled.

While certain specific relationships, materials and other parametershave been detailed in the above description of preferred embodiments,those can be varied, where suitable, with similar results. Otherapplications, variations and ramifications of the present invention willoccur to those skilled in the art upon reading the present disclosure.Those are intended to be included within the scope of this invention asdefined in the appended claims.

I claim:
 1. A method of making a spiral perfusion catheter assemblywhich comprises the steps of:providing an elongated catheter; mounting acatheter balloon on the distal end of said catheter substantiallycoaxial with said catheter, said catheter balloon configured with anexterior spiral lobe and channel pattern; forming a wire retainer from ashape memory alloy by heating an elongated segment of shape memory alloyabove the crystal phase change temperature for said shape memory alloy,shaping the wire retainer to have a central generally cylindrical spiralregion conforming to said spiral channel pattern and radially woundgenerally cylindrical end regions conforming to an outside diameter ofsaid catheter and cooling said segment to a temperature below saidcrystal change temperature; and unwinding said end regions sufficientlyto fit said end regions around said catheter adjacent to ends of saidballoon with said central region engaging said spiral channel pattern.2. The method according to claim 1 wherein said shape memory alloy isformed from a composition consisting essentially of nickel and titanium.3. The method according to claim 2 wherein said alloy is about 55.7 wt %nickel and about 43.9 wt % titanium.
 4. The method according to claim 1wherein said balloon has an axis and wire has a cross section width offrom about 0.02 to about 0.03 inch and thickness of from about 0.002 toabout 0.005 inch and said wire is wound with said width lying generallyparallel to said balloon axis.
 5. The method according to claim 4including the further step of rounding wire edges before said heatingstep.
 6. The method according to claim 1 wherein said radially wound endregions are wound in a contiguous relationship to form from about 1.5 to10 circumferential coils.
 7. The method according to claim 6, includingthe further step of encapsulating said radially wound end regions with amaterial selected from the group consisting of an adhesive, aheat-shrink plastic sleeve, tape and combinations thereof.